Overview: We are investigating the controls on nitrogen (N) cycling throughout the Ipswich River watershed in northeastern Massachusetts. The Ipswich River watershed landuse is a mix of urban, agrictultural, and reference types. To understand how aquatic networks control N exports, we require knowledge of what controls N reactivity across the entire range of river sizes that comprise the river network. Much research has been devoted to quantifying N cycle processes in small headwater streams, with a recent emphasis on denitrification. It remains unknown whether the controls in small streams apply to larger river reaches. In particular, the role of the hyporheic zone is potentially critical, yet scaling rules describing changes in transient storage zone/hyporheic characteristics and associated N cycle processes have yet to be determined.

Specific Objectives of this Project:1) Characterize the major interactions involving surface water hydraulics, hyporheic flow and nitrate concentrations in regulating rates of aquatic denitrification and nitrate retention across stream orders;

2) Determine how the spatial distribution of denitrification and nitrate retention interacts with the distribution of nitrate inputs to define river network control of N exports to the coastal zone.

This material is based upon work supported by the National Science Foundation under Grant No. DEB 06-14350. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.